The electric cable is constituted by: a central conductor surrounded by a plurality of layers constituting an insulation system; at least one metal screen connected to ground; and a protective outer sheath. In particular, the various components of the cable have the function of protecting people and animals against electrocution, of avoiding electric discharges in the medium surrounding the cable, such as air, and of minimizing energy losses while electricity is being transported. However, at the end of the cable, the central conductor under high voltage is at a distance of only a few millimeters from the metal screen connected to ground. This distance is much shorter than the breakdown voltage of the medium in which the end of the cable is situated (e.g. air), thereby leading to a short-circuit. Given the magnitude of the electric field existing in the insulating portions of a cable system, in particular in the vicinity of interfaces, it is necessary to control electric field density by arranging the end structures of cables under high voltage to comply with an additional constraint whereby the end of a cable must not be destroyed in the event of a voltage surge or an electric shock caused by lightning, for example.
Patent application WO 00/74191 A1 describes a high-voltage cable end structure comprising a resistive layer that surrounds the cable, and that is connected at one of its ends to the high-voltage, and at its other end to ground. A stress cone surrounds the resistive layer beside its portion connected to ground. However, that structure can lead to unsatisfactory performance in the event of a surge, or during operations such as circuit-breaking, or reversing polarity, for example.
Patent application FR 2 480 039 proposes using an electrode for reducing electrical stress at the edge of the screen, around the periphery of the insulator of the electrical conductor. The electrode comprises a plurality of contiguous zones presenting different resistances. The resistance of the stress electrode is selected to be non-linear. It varies as a function of the applied voltage, such that the magnitude of the current passing through the electrode does not vary linearly with the voltage. In addition, the stress electrode is floatingly mounted at one of its two ends. The structure proposed in that patent application presents the drawback of operating in unsatisfactory manner with DC.